1. Field of the Invention
The invention relates in general to a paper-separating plate with multi-stages. More particularly, the invention relates to a paper-separating plate suitable for a paper-seized mechanism of an automatic document feeder (ADF).
2. Description of the Related Art
An image input/output device, such as a copying machine, a facsimile machine or a scanner, is provided with  contains an image-input system. In general, a document is placed on a glass plate, and an optical system placed under the glass plate is used to read an image, such as words or figures. In case  When the dimensions of documents coincide, the image input/output device can be designed with an automatic document feeder matching the optical system. Therefore, by the automatic document feeder  Consequently, the documents can be transferred one by one and pass by  over the surface of the glass plate. Meanwhile , with the use of the automatic document feeder, and the images of the documents can be read by the linear scanning of the optical system. Also, the automatic  Automatic document feeders can be mounted on a printer, a copying machine, a facsimile machine, a scanner, or other machines  where a stake  stack of documents has to separates  are separated.
Currently, the automatic document feeder is provided with the paper-separating mechanism in order to transfer documents one by one to a scanning region of the optical system of the image input/output device. FIG. 1 is a cross-sectional view showing a known traditional paper-separating mechanism. A paper-separating mechanism 100 includes a paper-separating roller 110, a paper-feed roller 120 and a paper-separating plate 130. The paper-separating roller 110 and the paper-feed roller 120 are mounted in the automatic document feeder. The axis of the paper-separating roller 100 is substantially parallel with that of the paper-feed roller 120 and the rolling direction of the paper-separating roller 110 is the same as that of the paper-feed roller 120. Besides, the contact surface 132 of the paper-separating plate 130 is elastically pressed onto the bottom surface of both the paper-separating roller 110 and the paper-feed roller 120. For example, one end of the paper-separating plate 130 is pivoted on the automatic document feeder, as shown in the right portion of FIG. 1, while a spring 134 is mounted onto the other end of the paper-separating plate 130, as shown in the left portion of FIG. 1. As a result, the contact surface 132 of the paper-separating plate 130 can be elastically pressed onto the bottom surface of both the paper-separating roller 110 and the paper-feed roller 120.
The condition that  documents 10 are separated by the paper-separating mechanism 100 is that  when the friction (Fr) between the roller (the paper-separating roller 110 or the paper-feed roller 120) and documents 10 is larger than the friction (Fp) between the paper-separating plate 130 and documents 10 and that the friction (Fp) between the paper-separating plate 130 and documents 10 is larger that the friction (Fd) between documents 10. In other words, the condition that documents 10 are separated by the paper-separating mechanism 100 is “Fr>Fp>Fd”. When a stack of documents 10 is transferred into the paper-separating mechanism 100, a first paper-separating operation is performed using the paper-feed roller 120 and the paper-separating plate 130. In an ideal case, documents 10 should be transferred one by one to the space between the paper-separating roller 110 and the paper-separating plate 130 using the paper-feed roller 120 and the paper-separating plate 130. However, two or three sheets of documents 10 may be transferred to the space between the paper-separating roller 110 and the paper-separating plate 130. In the  that case, several sheets of documents 10 are first separated from a stack of documents 10 using the paper-feed roller 120 and the paper-separating plate 130. Subsequently, the several sheets of documents 10 first separated are transferred to the space between the paper-separating roller 110 and the paper-separating plate 130. Next, only one sheet of documents 10 is second  then separated from the several sheets of documents 10 first separated using the paper-separating roller 110 and the paper-separating plate 130 . However, provided that  if the condition of “Fr>Fp>Fd” is not satisfied, two or even more sheets of documents 10 can be output after documents 10 are separated using the paper-separating roller 110 of paper-separating mechanism 100 and the paper-separating plate 130. The  the documents 10 can not be separated one by one  from one another effectively.